Guarding ostrich, guarding dog (5)
I believe the answer is:
dingo
'dog' is the definition.
(I've seen this before)
'guarding ostrich guarding' is the wordplay.
'guarding' indicates the answer is hidden within the clue.
'DINGO' can be found hidden inside 'guarding ostrich'.
(Other definitions for dingo that I've seen before include "Wild dog of Australia" , "Wild creature" , "Yellow Australian dog" , "Wild dog of Oz" , "Scavenger" .)